Multistation computer systems are widely used because of the economies associated with using a single powerful processor to service the computation needs of a group of users. There are a vast number of such products, using a large number of different computer architectures. The present invention concerns one aspect of such computer architectures: the interconnections between the host computer and its workstations.
There are two primary classes of methods which are used to interconnect host computers to their workstations. First, there is the direct connection method in which each workstation is coupled by a cable to a port on the host computer. In this model, the host computer interacts with the workstation as it would with any other peripheral device. As a result, the length of the cable to the workstation is quite limited because of the need to limit the amount of time that the processor in the host computer can be forced to wait to execute standard transactions such as writing a byte or word of data in a workstation's video memory. Typical cable length restrictions range from 20 to 200 meters. The longer the cable to a workstation, the greater the impact that workstation has on the overall performance of the computer system. An advantage of this type of multistation computer system is that the workstations need not have any internal computational capability, allowing the use of relatively inexpensive workstations.
Second, there are multistation computer systems in which the host computer interacts with its workstations via a local area network. Local area networks (LANs) allow the workstations to be daisy chained together, thereby reducing the number of peripheral devices which are directly connected to the host computer. However, LANs requires a level of network software which significantly reduces the performance of the computer system and noticeably slows down the speed with which the host computer services the workstations. In addition, this type of multistation computer system requires the use of relatively expensive workstations which have their own CPUs because it is impractical to have a host computer service directly service hardware interrupts in workstations coupled to the host computer by a local area network.